Solar heater and method

ABSTRACT

A solar heater has a light collector which collects light incident on the light collector into a beam that extends along a beam axis. A plurality of thermally conductive plates is arranged along the beam axis, each of the plates having an aperture on the beam axis. For each plate, the aperture of the plate is smaller than apertures of all plates disposed between each plate and the light collector along said beam axis. A fluid pathway is associated with one or more of the plates for transferring heat to a fluid in the fluid pathway. In a related method of heating a fluid, light rays are collected into a beam and passed through progressively smaller apertures in a plurality of serially arranged plates such that a portion of the beam is incident on each one of said plates. The fluid is thermally contacted with the plates.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119(e) from provisional application No. 61/537,728.

BACKGROUND

The present invention relates to solar heaters and to methods of solar heating.

Given the environmental concerns arising from the use of fossil fuels and the environmental risks associated with the production of nuclear energy, there is an increasing interest in the use of “green” technologies for energy production. One green technology which has been subject of significant development is that of harnessing solar energy. There is therefore a continued need for improved approaches to harness solar energy.

SUMMARY

A solar heater and a solar heating method utilize a plurality of plates with apertures that decrease in size in a direction of propagation of a light beam.

According to an aspect, a solar heater has a light collector which collects light incident on the light collector into a beam that extends along a beam axis. A plurality of thermally conductive plates is arranged along the beam axis, each of the plates having an aperture on the beam axis. For each plate, the aperture of the plate is smaller than apertures of all plates disposed between each plate and the light collector along said beam axis. A fluid pathway is associated with one or more of the plates for transferring heat to a fluid in the fluid pathway.

According to another aspect, in a method of heating a fluid, light rays are collected into a beam and passed through progressively smaller apertures in a plurality of serially arranged plates such that a portion of the beam is incident on each one of said plates. The fluid is thermally contacted with the plates.

Other features and aspects of the invention will become apparent from the following description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate, by way of example only, embodiments of the present disclosure:

FIG. 1 is a schematic view of a solar heating system made in accordance with an embodiment;

FIG. 2 is a schematic view of a portion of the system of FIG. 1;

FIG. 3 a perspective view of a portion of the solar heating system of FIG. 1;

FIG. 4A is an exploded view of a portion of FIG. 2;

FIG. 4B is a schematic cross-sectional view of a portion of FIG. 2; and

FIG. 5 is an exploded view of a portion of a solar heating system made in accordance with another embodiment.

DETAILED DESCRIPTION

With reference to FIG. 1, an example solar heating system 10 for heating a working fluid has a solar heater 12 mounted through a positioning system 15 to support arm 16. A fluid conduit 14 which is connected to a cold fluid outlet 18 of a storage tank 20, runs to the solar heater 12, and a second fluid conduit 17 exits the heater and terminates at a hot fluid inlet 22 of storage tank 20. A back-up system 30 to solar heating system 10 is in heat exchange relationship with storage tank 20. A hot fluid outlet 24 of tank 20 may connect to an external system (not shown), such as a domestic heating system. The storage tank holds a working fluid, such as water. Back-up system 30 could include a back-up boiler and a back-up burner, such as a conventional oil or gas fired or electric burner.

A clevis 32 extending from the solar heater 12 is pivotably mounted at pivot 34 to base 36. The base 36 is in turn mounted to support arm 16 through a first pivot (not shown) so as to rotate about the longitudinal axis of the support arm and a second pivot (not shown) so as to tilt in a direction which is both perpendicular to the support axis and perpendicular to the axis of the pivot 34. Turning to FIG. 2, servo motor 38 of positioning system 15 acts to tilt the solar heater about pivot 34; servo motor 40 acts to tilt the solar heater about a pivot which is both perpendicular to the support axis and perpendicular to the axis of the pivot 34; and servo motor 42 acts to pivot the solar heater about the longitudinal axis of the support arm 16. The servo motors input computer-controller 44; the controller 44 also receives an input signal from solar intensity sensor 46.

The controller 44 operates to control the servo motors of positioning system 15 so as to orient solar heater 12 to follow the path of the sun. Thus, controller 44 and positioning system 15 act as a solar tracking system. Since solar tracking systems are conventional, the solar tracking system is believed to be within the skill of one skilled in the art and is not further described. Optionally, a photovoltaic panel (not shown) may be used to provide power to the controller and the servo motors.

As seen in FIG. 1, solar heater has a housing 26. FIG. 3 illustrates the solar heater 12 without this housing. With reference to FIG. 3, solar heater 12 includes a light collector in the nature of a focusing lens 50 supported by arms 52 at a stand-off from a heat exchanger 54. When facing the sun, the lens 50 directs light along a beam axis coincident with a central axis C and focuses this light at a focal point at heat exchanger 54. With reference to FIG. 4A, the heat exchanger 54 has upper housing cups 56 and 58 and lower housing disc 60 encasing a stack of plates 64 a, 64 b, and 64 c (collectively, plates 64) extending transversely of, and aligned along, central axis C. The upper housing cups 56, 58 and each plate 64 has a central aperture, collectively, apertures 68, centered on central axis C. The plates 64 are made of a thermally conductive material, such as metal, as, for example, aluminum.

The central aperture in each of the upper housing cups 56, 58 is larger than the aperture in top plate 64 a. As is most easily seen in FIG. 4B, each apertured plate 64 has a different sized aperture and the plates are arranged so that the apertures progressively decrease in size in a direction away from lens 50. Thus, plate 64 a, which is closest to lens 50, has the largest aperture 68 a; plate 64 b next closest to lens 50 has the second largest aperture 68 b, and plate 64 c the smallest aperture 68 c.

The underside of each plate 64 is etched to form a spiral pathway 70; when the plates 64 are sandwiched together as shown in FIG. 4B, the underside of each spiral pathway is closed off. An opening 72 through the top of middle plate 64 b communicates the outer end of the spiral pathway of the top plate with the outer end of the spiral pathway of the middle plate. An opening 74 through the top of the lower plate 64 c communications the inner end of the spiral pathway of the middle plate 64 b with the inner end of the spiral pathway of the lower plate 64 c. Aligned openings in housing disc 60 and plates 64 b, 64 c receive the end of conduit 17 which terminates at the inner end of the spiral pathway of the top plate 64 a. A further opening in the housing disc 60 receives conduit 14 which terminates at the outer end of the spiral pathway of the bottom plate 64 c.

It will be apparent from FIG. 4B that the stack of plates 64 extends a relatively short distance along the central axis C. Consequently, the lens 50 can have a focal plane somewhere within the heat exchanger and the light with be substantially in focus at each plate of the stack of plates. The characteristics of the lens are chosen such that sunlight focused by the lens 50 has, at each plate 64 a, 64 b, 64 c, a beamwidth greater than the diameter of the aperture 68 a, 68 b, 68 c through the plate.

In use, solar heater 12 is located in an area where it is exposed to sunlight. Controller 44 may then control servo motors 38, 40, and 42 in order to adjust the orientation of solar heater 12 through the day so that the lens 50 constantly faces the sun.

Since the apertures 68 of each successive plate 64 in a downstream direction decrease in size, for any given apertured plate downstream of plate 64 a, a peripheral portion of the part of the beam that passes through the aperture of the plate immediately upstream of the given plate will be incident on the given plate 64 while a central portion of the beam will pass through the aperture of this given plate. The portion of the beam passing through aperture 68 c of the last apertured plate 64 c is incident upon solid plate 60. Thus, it will be apparent that a portion of the light from the beam is incident on each one of plates 64.

The portion of the beam striking a plate 64 transfers energy to the plate, and therefore heats the plate. While the beam strikes only the more central region of a plate, since the plates are made of a thermally conductive material, this heat will diffuse across the plate.

As plates 64 are heated, working fluid within the spiral pathway 70 of each plate is heated. This reduces the density of the working fluid and will result in a convective flow through the conduit 14 from cold fluid outlet 18 of tank 20 to the hot fluid inlet 22 of the tank, given a judicious choice for the height of the cold fluid outlet 18 relative to the plates 64. Flow may be more readily assured if, as shown, the conduit 14 is connected so that fluid flowing from the cold fluid outlet 18 flows first through the spiral path 70 of the bottom plate 64 c. Alternatively, and especially if the conduit is connected so that fluid flowing from the cold fluid outlet 18 flows first through the spiral pathway 70 of the top plate 64 c, a pump (not shown) may be placed in fluid conduit 14 to pump fluid through the conduit 14 to hot fluid inlet 22.

The temperature at which working fluid is discharged from fluid conduit 14 depends on the quantity of solar energy collected by solar heater 12, the efficiency of heat transfer to the working fluid, and the flow rate of the working fluid, among other factors. The quantity of solar energy collected by solar heater 12 is directly proportional to the area of lens 50 and the intensity of the incident solar radiation.

Heated working fluid in tank 20 may be drawn off for use at the tank's hot fluid outlet 24.

In some circumstances, it may be desirable to supplement the supply of heated working fluid from the solar heater 12. For example, on a cloudy day, solar heater 12 may not heat the working fluid to the desired temperature. If this occurs, additional heating may be provided by back-up system 30. Back-up system 30 may be operated in parallel with solar heater 12, supplementing its output. The back-up system may also be operated when solar heater 12 inactive, such as at night.

The heated fluid produced by solar heating system 10 can be used for a variety of purposes. For example, heated fluid may be circulated through pipes and radiators in a building to provide heating for the building. Also, if the working fluid is water, solar heating system 10 may be used to provide a supply of warm or hot water for domestic use.

Optionally, lens 50 could be replaced with a different light collector, such as a reflector.

In another embodiment, with reference to FIG. 4, the solar heater 112 includes a collector 160, a collimator 162, and a heat exchanger 154 with a stack of plates 164 a, 164 b, 164 c, 164 d, and 164 e (collectively, plates 164) extending transversely of, and aligned along, a central axis C. Each plate, except plate 164 e, has a central aperture 168 a, 168 b, 168 c, and 168 d (collectively, apertures 168) centered on central axis C. In the example embodiment, collector 160 and collimator 162 are lenses positioned so that the collector lens has a focal point, F, located between the collector lens and the collimator lens and so that focal point F is also a focal point of the collimator lens. The heating power of solar heater 112 is proportional to the amount of solar radiation incident on collector 160, i.e., to the area of collector 160. Accordingly, collector 160 may be as large as available space permits.

Each apertured plate 164 has a different sized aperture and the plates are arranged so that the apertures progressively decrease in size in a direction away from collimator 162. Thus, plate 164 a, which is closest to collimator 162, has the largest aperture; plate 164 b next closest to collimator 162 has the second largest aperture, plate 164 c the next largest aperture, and plate 164 d the smallest aperture.

Fluid conduit 14 terminates at a coil 169 with a looped portion 170 lying on each plate 164; each looped portion may be soldered, or otherwise affixed, to the underlying plate. The coil, or at least each looped portion 170 of the coil, is formed of a thermally conductive material so as to permit heat transfer from the plates 164.

In use, collector lens 160 concentrates light by focusing it at focal point F and the light then diverges from this point and is collimated by the collimator lens. Collimator 162 collimates light into a beam having a beam axis coincident with central axis C. Collimator 162 is configured so that this beam has a diameter greater than that of the aperture 168 a in the topmost plate 164 a, such that a peripheral portion of the beam is incident on plate 164 a while the central portion of the beam passes through aperture 168 a.

Since the aperture 168 of each successive plate in a downstream direction decreases in size, for any given apertured plate downstream of plate 164 a, a peripheral portion of the part of the beam that passes through the aperture of the plate immediately upstream of the given plate will be incident on the given plate 164 while a central portion of the beam will pass through the aperture of this given plate. The portion of the beam passing through aperture 168 d of the last apertured plate 164 d is incident upon solid plate 164 e. Thus, it will be apparent that a portion of the light from the beam is incident on each one of plates 164.

The portion of the beam striking a plate 164 transfers energy to the plate, and therefore heats the plate. While the beam strikes only the more central region of a plate, since the plates are made of a thermally conductive material, this heat will diffuse across the plate and heat the working fluid in the loops 170 of coil 169.

In an alternate embodiment, the collecting lens could be replaced with a parabolic reflector disposed below a stack of plates and reflecting light back up through a lens-type collimator and through the stack of plates. With such an embodiment, the plate with the largest aperture would be at the bottom of the stack. In a further alternate embodiment, collimator 162 could be a reflector.

While in the illustrated embodiment the loops 170 of the coil lie on each plate, they could obviously instead be associated with the underside of each plate. While the loops 170 are depicted near the periphery of each plate, they could instead be located near the center of each plate, where the plate temperature is highest. In another embodiment, there could be multiple loops 170 on each plate.

For a given collector size, the quantity of solar energy transferred to a particular plate 164 is proportional to the size of the annular portion of the plate which is exposed to the beam. The relative sizes of successive apertures 168 can therefore be adjusted to control the peak temperature of each plate during operation in order to maximize the heat transfer to working fluid in the conduit 14.

While in the illustrated example embodiment of FIGS. 1 to 4 there are three plates and in the illustrated embodiment of FIG. 5 there are five plates, obviously a different number of plates may be used. Where, for example, the FIG. 5 embodiment were modified so that there are eleven plates, the plate closest to the collimator could have an aperture with a diameter of 1.1″ and each successive plate could have an aperture 0.1″ smaller such that the tenth plate has an aperture with a diameter of 0.2″. As with the embodiment of FIG. 5, the eleventh plate could be a solid plate (lacking an aperture).

While the apertures of the illustrated embodiments are circular, they could also have other shapes. Further, the apertures of the plates do not need to have identical shapes provided they are progressively smaller so as to permit a portion of the beam to strike each plate.

While the illustrated embodiment shows a single tank, optionally, there could be a cold fluid reservoir and a separate hot fluid reservoir. Moreover, if the working fluid is water, the cold fluid reservoir may be a naturally occurring reservoir such as a lake or other body of water. As a further option, there may be no hot fluid reservoir and instead heated fluid may simply be discharged to where it is to be used.

The solar tracking system of the example embodiment may be replaced with any suitable solar tracking system, Indeed, while not as efficient, for some applications, solar heater may be used without a solar tracking system.

An advantage of the present solar heating system is its compact horizontal extent, allowing the solar heater 12 or 112 to be placed in a number of constrained spaces.

Other modifications will be apparent to those skilled in the art; therefore, the invention is defined in the claims. 

What is claimed is:
 1. A solar heater comprising: a light collector which collects light incident on said light collector into a beam that extends along a beam axis; a plurality of thermally conductive plates arranged along said beam axis, each of said plates having an aperture on said beam axis, for each plate, said aperture of said each plate being smaller than apertures of all plates disposed between said each plate and said light collector along said beam axis; a fluid pathway associated with one or more of said plates for transferring heat to a fluid in said fluid pathway.
 2. The solar heater of claim 1, wherein each of said plates extend transversely of said beam axis.
 3. The solar heater of claim 2, further comprising a tracking system for orienting at least said collector relative to the position of the sun in the sky.
 4. The solar heater of claim 3, wherein said tracking system comprises a computer-controller.
 5. The solar heater of claim 1 further comprising an additional plate arranged along said beam axis adjacent a one of said plurality of plates having a smallest aperture of said apertures, said additional plate being a solid plate.
 7. The solar heater of claim 1 wherein said fluid pathway is a spiral pathway formed in at least one of said plurality of plates.
 8. The solar heater of claim 7 wherein one said spiral pathway is formed on an underside of each of said plurality of plates.
 9. The solar heater of claim 8 further comprising an opening from one end of said spiral pathway of one plate to one end of said spiral pathway of an adjacent plate.
 10. The solar heater of claim 1 wherein said fluid pathway is a looped conduit lying on at least one of said plurality of plates.
 11. The solar heater of claim 1 wherein said plates are metal.
 12. A method of heating a fluid, said method comprising: collecting light rays into a beam; passing said beam through progressively smaller apertures in a plurality of serially arranged plates such that a portion of said beam is incident on each one of said plates; thermally contacting said fluid with said plates.
 13. The method of claim 12 wherein said apertures progressively decrease in size in the direction of propagation of said beam.
 14. The method of claim 13, wherein said thermally contacting comprises providing a spiral pathway on each of said plates. 